A worker grasps a newly poured and cleaned gold bar at the Driefontein Gold Mine southwest of Johannesburg, South Africa, on March 17, 2005.

The mine's owner, Gold Fields Ltd, produces 4.3 million ounces (122 million grams) of gold a year. New analyses of resources in South Africa suggest that shallow gold reserves have already been tapped.

But recently, gold hit a 28-year high: 770 U.S. dollars per ounce. The spike in value has sent mining companies scrambling to dig "ultra deep" mining shafts in South Africa and around the world, experts say.